Observation deck and external elevator plans revealed for Aon Center

601W Cos. has released renderings for the previously announced observation deck atop Chicago’s Aon Center. The space would be the city’s third observation deck—after Willis Tower’s Skydeck and the former John Hancock Center’s 360 Chicago—making Chicago the only American city outside New York with three such spaces.

Designed by Pasadena, California-based Hettema Group, the firm behind New York’s One World Trade Center observatory, the new attraction would include a few design changes to Chicago’s third-tallest structure. Some steel columns and granite cladding would be removed from the building’s exterior above the 82nd floor to provide uninterrupted vistas. The observatory would be accessed by an external, glass elevator installed in the high-rise’s northwest corner. It would be the tallest such elevator in the world.

Just as the Skydeck and 360 Chicago have competed with recently added attractions the Ledge and Tilt, respectively, the Aon Center’s observation deck will also include a feature to give tourists an outside-the-box experience. The plans call for a gondola on the roof, accessible via the 82nd-floor observatory for an additional fee, that would lower up to 22 guests at a time over the building’s edge.

The attraction would cost an estimated $185 million and two years’s construction to complete. Formerly known as the Standard Oil Building, the Aon Center was built in 1972. The New York-based 601W Cos. acquired the property in 2015 and began a $25 million renovation last year.